Lambeth residents who live and work in Oval are being asked to get a Covid-19 test after the South African variant was detected in the area.
The variant has already been found in parts of West Norwood and some streets in Streatham. The case was not linked to travel so public health officials are trying to find out if there are any more cases in the area.
Anyone in the affected area should get a test whether they have symptoms or not.
The enhanced testing programme, which includes genomic sequencing to identify which variant of the virus is present, applies to homes in postcodes SW8 1, SW9 0 and SW9 6B.
Mobile Testing Units (MTUs) will be deployed offering PCR testing, while home testing kits will also be provided.
If someone tests positive, they must self-isolate immediately and pass on details of anyone they have been in contact with to NHS Test and Trace when requested.
Some research has shown that the current vaccines may be less effective against the South African variant, though the ones being used now should still protect against serious illness.
Scientists are currently developing booster jabs to tackle Covid-19 variants.
Lambeth leader Councillor Jack Hopkins said: “There will be concern in our communities that there have now been two cases of this new strain of Covid-19 in Lambeth.
“I want to reassure people that these are separate cases, and that this enhanced testing is to better understand the variant, as well as identifying if there are any more cases in the area.
“I want to thank all Lambeth residents for following the current restrictions. We are now urging everyone living or working in the area with or without symptoms to get tested.
“The government has told us that there is currently no evidence that this variant causes more severe illness or that the regulated vaccine would not protect against it.
“Other than getting tested or other essential reasons, all residents are urged to follow the lockdown rules and stay at home, wash your hands regularly, keep your distance from others and wear a face covering.”
Professor Kevin Fenton, London regional director at Public Health England, said: “The UK has one of the best genomic systems in the world which has allowed us to detect the variant originating in South Africa here in London.
“I urge everyone offered a test to take it up to help us to monitor the virus in our communities and to help suppress and control the spread of this variant.
“The most important thing is that people continue to follow the national lockdown guidance that is in place – stay at home as much as possible, limit your number of contacts, wash your hands regularly and thoroughly, keep your distance and cover your face. If you test positive by any method, you must isolate to stop the spread of the virus.”